Internal combustion engines rely on valve actuation systems to control engine intake and exhaust valves, which in turn, control the flow of combustion components and products into and out of combustion chambers during operation. In a four-stroke operating cycle, intake valves are opened to admit fuel and air into an expanding combustion chamber during an intake stroke of a piston moving within a cylinder. In a compression stroke, the intake valves are closed and combustion components are compressed by the piston. The compressed combustion components are then ignited, causing a power stroke of the piston. In an exhaust stroke, exhaust valves are opened to allow combustion products to escape the cylinder as the piston is displaced therein. This operation is typically called a “positive power” operation of the engine and the motions applied to the valves during positive power operation are typically referred to as “main event” valve actuation motions. In addition to main event actuation, engine valve actuation systems may include features that facilitate auxiliary valve actuation motion to support functions such as engine braking (power absorbing), exhaust gas recirculation (EGR) and others. Such valve motion may be accomplished using “auxiliary” events imparted to one or more of the engine valves.
Valve movement is typically controlled by one or more rotating cams as motion sources. Cam followers, push rods, rocker arms and other elements, which may form a valvetrain, provide for direct transfer of motion from the cam surface to the valves. For auxiliary events, “lost motion” devices or variable length actuators may be utilized in the valvetrain to facilitate auxiliary event valve movement. Lost motion devices refer to a class of technical solutions in which valve motion is modified compared to the motion that would otherwise occur as a result of actuation by a respective cam surface alone. Lost motion devices may include devices whose length, rigidity or compressibility is varied and controlled in order to facilitate the selective occurrence of auxiliary events in addition to, or as an alternative to, main event operation of valves.
Auxiliary motion valve systems may utilize a dedicated rocker arm to support auxiliary events on one or more engine valves. In such systems, main event motion is facilitated by a main event rocker, while auxiliary motion is facilitated by the dedicated rocker, which is typically driven by a dedicated motion source, such as a cam. The dedicated rocker may include a piston actuator that is controlled to absorb or transfer motion. When the piston actuator is active (e.g., in an extended configuration), the dedicated rocker arm is said to be in an active state, and passes motion from a braking cam on to a motion receiving component, such as an engine valve. When the piston actuator is inactive (e.g., in a retracted configuration), the dedicated rocker is said to be in an inactive state. In the inactive state, the rocker may be disengaged from the braking cam as well as the valve. As such, the dedicated rocker may be in an uncontrolled state.
In conventional valvetrains, utilizing a cam follower and biasing mechanisms, such as valve springs or external springs, the rocker arm may operate in an controlled state where damage of motion imparting components (i.e., cam or cam surface) and motion receiving elements (engine valve or push rod. For example, at high operating speeds, acceleration of the cam and valvetrain components, combined with inertia of these components and the rocker arm, may cause separation between components in the valvetrain, such as the rocker arm, that should normally be in contact. This separation and the subsequent recontact of the components may result in damage to valvetrain contact surfaces and components and, in some cases, even possible contact between engine valves and pistons.
Prior art control devices have utilized biasing devices to provide some degree of control by biasing the cam follower end of a rocker toward the cam. In typical dedicated rocker systems, however, it is ordinarily not feasible to control rocker motion by providing a biasing force in an opposed direction, i.e., biasing the valve end of the rocker toward the valve and the cam follower end of the rocker away from the cam. This is because such configurations would cause the rocker to “chase” the valve or motion receiving component when the valve is subjected to main event motion via, for example, a valve bridge as known in the art.
In systems that incorporate variable valve actuation components, which may have active and inactive states, maintaining controlled operation of the rocker arm may be even more important. In a valvetrain with a variable actuator in a deactivated state, there may be more clearance between components in a valvetrain. As such, an uncontrolled rocker arm may compound the potential for contact surfaces to “chase” or become separated during operation, leading to high impact forces upon recontact and excessive wear and/or damage to components.
It would therefore be advantageous to provide systems that address the aforementioned shortcoming and others in the prior art.